Started: 2012-04-18 22:26:37
Last activity: 2012-04-19 16:02:21
Topics:
Carl Tape
2012-04-18 22:26:37
Dear sac-help:

I was wondering if you could clarify the convention for CMPINC.

CMPINC is define here
http://www.iris.edu/software/sac/manual/file_format.html as "Component
incident angle (degrees from vertical).

vang in the antelope schema is defined as:
This attribute measures the angle between the sensitive axis of a
seismometer and the outward-pointing vertical direction. For a vertically
oriented seismometer, vang = 0, or 180 (to reverse the sense of the
instrument). For a horizontally oriented seismometer, vang = 90. See hang.

The definition for CMPINC is somewhat ambiguous, since "vertical" is a
line, not a vector. Does "vertical" mean "outward-pointing vertical
direction"?

Thanks,
Carl

• Yingcai Zheng
2012-04-19 03:06:00
upward : cmpinc = 0
downward: cmpinc = 180

north component: cmpinc = 90
east component: compinc = 90

also :

cmpaz =0 for north component
cmpaz=90 for east component

am i right?

Yingcai zheng

mit

On Wed, Apr 18, 2012 at 7:26 PM, Carl Tape <carltape<at>gi.alaska.edu> wrote:

Dear sac-help:

I was wondering if you could clarify the convention for CMPINC.

CMPINC is define here
http://www.iris.edu/software/sac/manual/file_format.html as "Component
incident angle (degrees from vertical).

vang in the antelope schema is defined as:
This attribute measures the angle between the sensitive axis of a
seismometer and the outward-pointing vertical direction. For a vertically
oriented seismometer, vang = 0, or 180 (to reverse the sense of the
instrument). For a horizontally oriented seismometer, vang = 90. See hang.

The definition for CMPINC is somewhat ambiguous, since "vertical" is a
line, not a vector. Does "vertical" mean "outward-pointing vertical
direction"?

Thanks,
Carl

_______________________________________________
sac-help mailing list
sac-help<at>iris.washington.edu
http://www.iris.washington.edu/mailman/listinfo/sac-help

2012-04-19 00:19:31

The below outline matches my understanding of the common usage, basically vertical is positive up or "outward-pointing". This also matches the convention implied when the DMC converts a SEED dip to a SAC inclination.

IRIS DMC

On Apr 18, 2012, at 5:06 PM, Yingcai Zheng wrote:

upward : cmpinc = 0
downward: cmpinc = 180

north component: cmpinc = 90
east component: compinc = 90

also :

cmpaz =0 for north component
cmpaz=90 for east component

am i right?

Yingcai zheng

mit

On Wed, Apr 18, 2012 at 7:26 PM, Carl Tape <carltape<at>gi.alaska.edu> wrote:
Dear sac-help:

I was wondering if you could clarify the convention for CMPINC.

CMPINC is define here http://www.iris.edu/software/sac/manual/file_format.html as "Component incident angle (degrees from vertical).

vang in the antelope schema is defined as:
This attribute measures the angle between the sensitive axis of a seismometer and the outward-pointing vertical direction. For a vertically oriented seismometer, vang = 0, or 180 (to reverse the sense of the instrument). For a horizontally oriented seismometer, vang = 90. See hang.

The definition for CMPINC is somewhat ambiguous, since "vertical" is a line, not a vector. Does "vertical" mean "outward-pointing vertical direction"?

Thanks,
Carl

_______________________________________________
sac-help mailing list
sac-help<at>iris.washington.edu
http://www.iris.washington.edu/mailman/listinfo/sac-help

_______________________________________________
sac-help mailing list
sac-help<at>iris.washington.edu
http://www.iris.washington.edu/mailman/listinfo/sac-help

• Carl Tape
2012-04-19 16:02:21
Thanks, folks. I suppose the only concrete change would be to add a word or
two to the manual definition of CMPINC, like "upward-pointing vertical
direction" or "outward-pointing vertical direction".

Thanks,
Carl

The below outline matches my understanding of the common usage, basically
vertical is positive up or "outward-pointing". This also matches the
convention implied when the DMC converts a SEED dip to a SAC inclination.

IRIS DMC

On Apr 18, 2012, at 5:06 PM, Yingcai Zheng wrote:

upward : cmpinc = 0
downward: cmpinc = 180

north component: cmpinc = 90
east component: compinc = 90

also :

cmpaz =0 for north component
cmpaz=90 for east component

am i right?

Yingcai zheng

mit

On Wed, Apr 18, 2012 at 7:26 PM, Carl Tape <carltape<at>gi.alaska.edu> wrote:

Dear sac-help:

I was wondering if you could clarify the convention for CMPINC.

CMPINC is define here
http://www.iris.edu/software/sac/manual/file_format.html as "Component
incident angle (degrees from vertical).

vang in the antelope schema is defined as:
This attribute measures the angle between the sensitive axis of a
seismometer and the outward-pointing vertical direction. For a vertically
oriented seismometer, vang = 0, or 180 (to reverse the sense of the
instrument). For a horizontally oriented seismometer, vang = 90. See hang.

The definition for CMPINC is somewhat ambiguous, since "vertical" is a
line, not a vector. Does "vertical" mean "outward-pointing vertical
direction"?

Thanks,
Carl

_______________________________________________
sac-help mailing list
sac-help<at>iris.washington.edu
http://www.iris.washington.edu/mailman/listinfo/sac-help

_______________________________________________
sac-help mailing list
sac-help<at>iris.washington.edu
http://www.iris.washington.edu/mailman/listinfo/sac-help

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